Process of separating hydrocarbons



Patented Jan. 1, 1946 PROCESS OF SEPABATING HYDROCABBONS Charles E. Welling, Bartlesvllle, kla., asslgnor to Phillips Petroleum Company, a corporation of Delaware N 0 Drawing. Application February 2, 1942,

Serial No. 429,341

Claims. (Cl. 183-115) This invention relates to a process for separating aliphatic hydrocarbons and is particularly concerned with the separation of unsaturated aliphatic hydrocarbons from saturated aliphatic hydrocarbons and with the separation of aliphatic hydrocarbons of varying degrees of unsaturation by selective solution in a liquid solvent.

It is the principal object of this invention to effectively separate mixtures of unsaturated and saturated aliphatic hydrocarbons which are not capable of being conveniently separated by ordinary fractional distillation.

Another object of this invention is to effectively separate mixtures of aliphatic hydrocarbons of varying degrees of unsaturation which cannot be properly separated by usual fractional distillation. I

This invention has for a further object the provision of a satisfactory and economical process for'separa-ting mixtures of paraillns, olefins and diolefins, especially those which have from four to six carbon atoms per molecule and which are not readily separated by ordinary fractional distillatiorr.

In the various processes of converting hydrocarbons, such as cracking normally gaseous hydrocarbons or oils, or in processes for. the production of oleflns or dioleflns, there will frequently be formed mixtures which may contain some or all of the types of aliphatic hydrocarbonsknown as parafllns, olefins, and diolefins. Such mixtures may usually be separated by fractional distillation into fractions consisting essentially of hydrocarbons of the same number of carbon atoms per molecule. but the further separation of such fractions to obtain reasonably pure diolefins or olefins, as is frequently desirable, is often very difficult by conventional fractionation. This difficulty is due to the fact that the boiling points of diolefin, olefin, and paraffin hydrocarbons which have the same number of carbon atoms per molecule are ordinarily relatively close together. Thus, for example, isobutene, l-butene, butadiene, and n-butane all boil within a range of eight degrees centigrade.

I have discovered that a satisfactory separation of a mixture of diiferent types of close-boilin aliphatic hydrocarbons, particularly those having from four to six carbon atoms to the molecule, such as diolefins, olefins, and paraillns, may be obtained by treating such a mixture in the gaseous state with a liquid solvent chosen from the ployed in the practice of my invention, the all-- phatic esters of levulinic acid, and especially the aliphatic esters consisting of butyl le'vulinate' and lower, are best suited to effectively and economically accomplish objects of my instant invention.

When such mixtures of hydrocarbons are main tained in the gaseous state and contacted with some solvent chosen from the above named group, any diolefln present is-preferentially dissolved in the solvent, olefins present are dissolved to a lesser degree, and paralllns are still less soluble.

My invention maybe carried out by contactin the gaseous hydrocarbon mixture with a portion of the liquid solvent under suitable conditions of temperature and pressure and then separating the liquid and gaseous phases. The gaseous phase will then be found to be impoverished in diolefins" and perhaps to some extent in oleilns. The hydrocarbons dissolved'in the solvent may be recovered by application of heat or reduction of pressure or by other means known in the art. These dissolved hydrocarbons when recovered will be found to have an enhanced content of dioleflns and possibly of olefins. If desired, such a batchwise operation may be repeated several times in order to obtain a more complete separation of the components of the original hydrocarbon mixture.

I may also apply my invention by flowing the gaseous hydrocarbon mixture in countercurren't to a stream of some solvent chosen from the I above named group of solvents, utilizing any group of relatively non-volatile solvents consisting of levulinic acid and an ester of levulinic acid. While various esters of levulinic acid may be emmeans known in the art for securing good contactlag between counterflowing liquid and gas streams such as packed or bubble plate columns. In using a column for this purpose, the solvent stream would be introduced at or near the top of the column while they gaseous hydrocai'bon mixture to be treated would be introduced at some intermediate point along the column or near the bottom. The upflowing stream of hydrocarbon vapors would be scrubbed by the downflowing solvent and the more soluble constituents dissolved in the solvent. Solvent reaching the kettle of the column would be removed and then treated in some known manner to stri out the dissolved hydrocarbons and then the stripped solvent could be recycled. The less soluble constituents of the original hydrocarbon mixture would not be dissolved in passing up through the column and could be withdrawn at the top of the column.-

The conditions of temperature and pressureat which I practice my process are somewhat dependent upon the hydrocarbon mixture to be treated. It will usually be desirable to work at temperatures within the range of-about to about 300 F., and the pressure can be so adjusted that for a particular temperature and hydrocarbon mixture a gaseous phase will be maintained.

The amount'of solvent to be used in treating a given amount of a hydrocarbon mixture will depend. upon such factors as the specific components of the hydrocarbon mixture and the degree of separation that is desired and the characteristics of the specific apparatus that is employed such as the height or efficiency of a contacting tower.

Any individual solvent from the group consistin: of levulinic acid and the esters of levulinic acid, such as the aliphatic esters, may be employed in practicing my invention or a mixture of two or more of the esters may be used. Under some circumstances, it may be desirable to supply means for maintaining the pH- of the ester type solvents near the point of neutrality in order to minimize any tendency, for hydrolysis of the esters.

Some differences exist among the various solvents in the group named. Thus, I have found levulinic acid to show extremely high selectivity while the aliphatic esters of levulinic acid show somewhat lower selectivity but higher solubility for the hydrocarbon, mixtures I propose to treat according to my invention.

In the manner described above, diolefins may be separated from oleiins or from paramns and oleflns, or olefins may be separated from parafllns. Likewise, a mixture of diolefins and oleflns may be separated from parafllns. Specific mixtures which may be treated according to my process are, for example, mixtures-of butanes and butenes, or mixtures of butadiene and l-butene, or mixtures of isoprene and pentane or mixtures of 2,3-did per-'f methy1-1.3-butadiene and hexane.

In order to show the efficacy of my process in separating hydrocarbon mixturesof the character indicated above, the following examples are cited, but it is to be understood that the invention is not limited thereto.

Example I Commercial levulinic acid, containing about 99 percent acid, was brought into contact with a were separated and the dissolved hydrocarbons dissolved hydrocarbons that were recovered from the solvent was found to be: butadiene, 3'7 mole per cent; l-butene, 47 mole per cent; n-butane, 16 mole per cent. By repeating the operation a further separation of the original hydrocarbon mixture could have been attained. The levulinic acid phase was found to contain about 8 mole per cent dissolved hydrocarbons when the phases were separated.

Example II Methyl levulinate was brought into contact with a. gaseous hydrocarbon mixture containing 25 mole per cent butadiene, 51-mole per cent 1- butene, and 24 mole per cent n-butane. After establishing equilibrium between the gasand liqing of levulinic acid and the lower aliphatic alkyl uid phases at a temperature of 200 F., and at a pressure of lbs. per sq. in. gauge, the phases recovered from the solvent by heating and reduc.. tionof pressure. The .composition of the gaseous hydrocarbon phase separated was foundto be: butadiene, 21 mole per cent; l-butene, 52 mole per cent; n-butane, 27 mole per cent. The composition of the dissolved hydrocarbons that were recovered from the solvent was found to be: butadiene, 30 mole per cent; l-butene, 50 mole per cent; n-butane, 20 mole per cent. By repeating the operation a further separation of the original hydrocarbon mixture could have been attained. The methyl levulinate phase was found to contain about 21'mole per cent dissolved hydrocarbons when the phases were separated.

From the foregoing, it is believed that the many advantages obtainable by the practice of the present invention will be readily apparent to persons skilled in the art. However, since certain changes may be made in carrying out the above method without departing from the scope of the invention'as defined by the appended claims, it is intendedthat all matter contained hereinshall be interpreted as illustrative and explanatory, rather than in a limiting sense.

'I claim: l 1. The method of separating close-boiling mixtures of aliphatic C4 to Ca hydrocarbons having similar boiling points and of varying degrees of V saturation, said mixture being composed of hydrocarbons having the same number of, carbon atoms per molecule, which comprises intimately contacting said mixture in the gaseous state with a liquid solvent selected from the group consisting of levulinic acid and the lower aliphatic alkyl esters of levulinic acid ranging up to the butyl esterand thereby effecting preferential dissolution in said solvent of the less saturated aliphatic hydrocarbon content of said mixture, separating the resulting liquid and gaseous phases, and recovering from the separated liquid phase said less saturated aliphatic hydrocarbon dissolved therein.

2. The method of separating close-boiling mixtures of aliphatic C4 to C6 hydrocarbons having similar boiling points and of varying degrees of saturation, said mnrture being composed of hydrocarbons having the same number of carbon atoms per molecule and comprising an aliphatic conjugated diolefln and a more'saturatedaliphatic hydrocanbon, which comprises intimately contacting said mixture in the gaseous state with a liquid solvent selected from the group consisting of levulinic acid and the lower aliphatic alkyl esters of levulinic acid ranging up to the butyl ester and. thereby efiecting preferential disso1u-.

tion in said solvent of said diolefin, separating the resulting liquid and gaseous phases, and recovering from the separated liquid phase said diolefin dissolved therein.

3. The method of separating a mixture of butadiene and a normal butenewhich comprises in-' 4. The method of separating a mixture of butadiene and l-butene which comprises intimately contacting said mixture in. the gaseous state with a liquid solvent selected from the group consistesters of levulinic acid ranging up to the butyl ester and thereby effecting preferential dissolu--- tion in said of the butadiene contained in said mixture, separating the resulting liquid and gaseous phases, and recovering hour the sepsrated liquid phase said butadiene dissolved therein.

5. The method or sep rating a mixture of isoprene and pentane which comilflfi s intimately contacting said mixture in the gaseous state with a liquid solvent selected irom the group consisting or levulinlc acid and the lower sliphstie slkyl esters of levulinic acid ringing up to the ,butyi ester and thereby eflecting preferential dissolution in said solvent of isoprene contained in said mixture, separating the resulting liquid and gaseous phases and recovering from the separated liquid phase said isoprene dissolved therein.

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